“I am concerned that this advertisement may reflect that Suburban Express is discriminating against potential customers,” Madigan said in a prepared statement. “Under the law, access to transportation must not be impacted or based on a person’s race or national origin. My office is investigating to determine whether Suburban Express’ policies and practices violate the law.”

The company has 30 days to comply with the subpoena, which requires it to turn over documents, records and information to aid the investigation.

Madigan’s Civil Rights Bureau issued the subpoena, which enforces state and federal civil rights laws to prohibit discrimination in Illinois and to advocate for legislation to strengthen the laws.

Madigan’s office is encouraging anyone who wants to file a complaint. People can do so online or by calling the Civil Rights Hotline at (877) 581-3692.

Bureau Chief Karyn Bass Ehler and Assistant Attorney General Cynthia Flores are in charge of the investigation.

Ameya Pawar, alderman for the 47th Ward of the City of Chicago, sent out a tweet Monday calling for a hearing to investigate the behavior of Suburban Express.

Dear Suburban Express: This is not an apology. This is an unbelievably offensive and bigoted response. Shame on you. Since you serve O'Hare International Airport, I am going to call for a hearing on your business practices. In them meantime, you may want to issue a real apology. pic.twitter.com/kNFkM1e0BW

“Since you serve O’Hare International Airport, I am going to call for a hearing on your business practices,” he said.

Suburban Express released a statement on its Facebook page Monday referencing Pawar’s tweet. The statement said the company has reached out to Pawar.

This is Suburban Express’s third apology following Saturday’s email advertisement.

“We screwed up and we know it. Our apology was inadequate. We hope to open a dialogue with Alderman Pawar about our shortcomings and how to make our services more inclusive in the future,” the Facebook post said.